Method and apparatus for forming substantially plate-like ceramic articles

ABSTRACT

A method for forming plate-like ceramic articles, comprising at least one step for deposition by pouring of at least one layer of a ceramic mixture that comprises an aqueous vehicle on a substantially absorbent transfer surface adapted to draw the aqueous vehicle, at least one step for drying so as to obtain a continuous material strand, and a cutting step for cutting the strand into a plurality of ceramic articles. An apparatus for performing the method comprising a framework for supporting an absorbent transfer surface, at least one unit for depositing at least one mixture layer onto the surface, at least one drying unit for at least partial drying of the mixture layer to obtain a continuous strand of plastic ceramic material, and a cutting unit.

[0001] The present invention relates to a method for formingsubstantially plate-like ceramic articles and to the apparatus forcarrying out the method.

BACKGROUND OF THE INVENTION

[0002] It is known that various technologies are used in the ceramicssector to manufacture ceramic articles such as tiles and the like andcan be distinguished substantially according to the forming method thatthey use.

[0003] Forming by pressing is known, for example, and generally providesfor the wet milling of the raw materials in drum mills in order toobtain an aqueous suspension of milled solid particles that isconventionally known as slurry.

[0004] The resulting slurry is discharged from the mill and deposited indedicated tanks, which are provided with means for moving said slurryand in which, in the case of the manufacture of porcelain stonewarearticles, it is possible to add appropriately milled coloring oxides inorder to obtain slurries having various colors.

[0005] The slurry is then dried inside spray driers in order to obtainpowders that have a controlled degree of humidity, which are fed towardthe article forming presses after a settling and homogenization step.

[0006] As an alternative, it is also known to form articles byextrusion; this method uses slurries that are first filtered withinappropriately provided filter presses in order to obtain a plasticpaste.

[0007] Said plastic paste is then extruded through dies, from which itexits as a continuous strand to be cut into articles having the chosendimensions.

[0008] Regardless of whether forming has occurred by pressing or byextrusion, the resulting articles are fired in a kiln, after optionalsurface decoration and/or glazing.

[0009] However, these known methods are not free from drawbacks,including the fact that the slurries discharged from the mills must besubjected to an intermediate treatment (drying or filtering) performedbefore forming the articles, and said treatment requires theavailability of dedicated equipment and entails structural complicationsof the production facilities, an increase in the installation andrunning costs of said facilities, an increased length and reduced speedof production lines, and an increase in labor costs and energyconsumption.

[0010] Moreover, particularly in the case of forming porcelain stonewarearticles by pressing, managing powders in different colors, formatsand/or particle sizes is rather complicated and expensive.

[0011] To obviate these drawbacks, a method for forming ceramic articlesis also known which essentially consists in depositing in succession ona porous working surface a plurality of uniform layers of a fluidmixture of ceramic material, each layer being deposited on the previousone after drying the latter by heating it.

[0012] In particular, the drying step consists in transferring heat byconvection and/or radiation to the intermediate component beingproduced, so as to achieve evaporation of the moisture contained in thefreshly deposited layer.

[0013] However, even this known method is susceptible of furtherimprovements aimed in particular at reducing the operating temperatures,in order to avoid the formation of defects in the resulting articlescaused by expansion of air microbubbles retained in the deposited layersand/or by the boiling of the water contained inside the intermediatecomponents being processed, and to contain energy consumption.

SUMMARY OF THE INVENTION

[0014] The aim of the present invention is to provide a method andapparatus for forming, at reduced temperatures, and anyway such as toavoid formation of defects, substantially plate-like ceramic articles.

[0015] Within this aim, an object of the present invention is to providea method that is simple, relatively easy to provide in practice, safe inuse, effective in operation, and has a relatively low cost.

[0016] This aim and this and other objects that will become betterapparent hereinafter are achieved by the present method for formingsubstantially plate-like ceramic articles, characterized in that itcomprises at least one step for deposition by pouring of at least onelayer of a ceramic mixture that comprises an aqueous vehicle on asubstantially absorbent transfer surface suitable to draw said aqueousvehicle, at least one step for drying at least the lower portion of saidsurface so as to achieve at least partial evaporation of the aqueousvehicle absorbed by said surface, with consequent at least partialdrying of said layer in order to obtain a continuous strand of plasticceramic material, and a step for cutting said strand into a plurality ofceramic articles.

[0017] This aim and this and other objects that will become betterapparent hereinafter are further achieved by an apparatus for performingthe method according to the invention, characterized in that itcomprises a framework for supporting a substantially absorbent transfersurface, at least one unit for depositing, by pouring onto said surface,at least one layer of a ceramic mixture that comprises an aqueousvehicle, at least one unit for drying at least the lower portion of saidsurface so as to achieve at least partial evaporation of the aqueousvehicle absorbed by said surface, with consequent at least partialdrying of said layer in order to obtain a continuous strand of plasticceramic material, and a unit for cutting said strand into a plurality ofceramic articles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further characteristics and advantages of the present inventionwill become better apparent from the following detailed description ofsome preferred but not exclusive embodiments of a method for formingsubstantially plate-like ceramic articles and of the associatedapparatus, illustrated by way of non-limiting example in theaccompanying drawings, wherein:

[0019]FIG. 1 is a schematic partial side view of a first embodiment ofthe apparatus for performing the method according to the invention;

[0020]FIG. 2 is a sectional view, taken along the line II-II of FIG. 1;

[0021]FIG. 3 is a transverse sectional view of a first embodiment of thetransfer surface of the apparatus according to the invention;

[0022]FIG. 4 is a transverse sectional view of a second embodiment ofthe transfer surface of the apparatus according to the invention;

[0023]FIG. 5 is a partial schematic side view of a second embodiment ofthe apparatus for performing the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] With reference to the figures, the reference numeral 1 generallydesignates an apparatus for forming substantially plate-like orplate-shaped ceramic articles, particularly tiles and the like.

[0025] The apparatus 1 comprises a framework 2 for supporting ahorizontal surface 3 for transfer along an advancement direction,designated by the arrows A in the figures, which is of a substantiallyabsorbent type, at least one unit 4 for depositing by pouring a layer 5of a ceramic mixture that comprises an aqueous vehicle on the surface 3,and at least one unit 6 for drying the lower portion of the surface 3 soas to achieve at least partial evaporation of the aqueous vehicleabsorbed by said surface, with consequent at least partial drying of thelayer 5, in order to obtain a continuous strand 7 of plastic ceramicmaterial.

[0026] The apparatus 1 further comprises, downstream of the drying unit6, a conventional cutting unit CU for cutting the strand 7 into aplurality of ceramic articles such as tiles or the like.

[0027] Such cutting unit CU can be provided directly on the surface 3 oron an auxiliary working surface not shown in the figures.

[0028] In this last case it is possible to provide means for theautomatic transfer of portions of the strand 7 from the surface 3 to theauxiliary surface.

[0029] As an alternative, the cutting unit CU can have pre-cutting meanson the surface 3 and means for finishing the cutting process on theauxiliary surface.

[0030] The ceramic mixture that is used is constituted for example by aconventional slurry, which comprises an aqueous suspension of ceramicraw materials in powder form, obtained according to the conventionaloperating method.

[0031] In the illustrated embodiments, the apparatus 1 has a depositionunit 4 and a drying unit 6, which is arranged on the surface 3downstream of said deposition unit along the advancement direction A;the strand 7 is formed starting from a single layer 5.

[0032] However, alternative embodiments of the apparatus 1 are alsopossible in which there are a plurality of units 4 for depositingrespective layers 5, the first mixture layer 5 being deposited on thesurface 3 and each successive layer 5 being superimposed on thepreviously deposited layer 5.

[0033] In this case, the strand 7 is formed starting from a plurality ofmutually superimposed layers 5 constituted by respective ceramicmixtures, which may optionally be different from one another.

[0034] The apparatus 1 may have a single drying unit 6, which runssubstantially along the entire length of the surface 3, or a pluralityof drying units 6, which are distributed along said surface andcooperate with respective deposition units 4.

[0035] The drying of the surface 3 reduces the content of aqueousvehicle retained by the porosities of said surface, so that the surface3 does not reach saturation and continues to draw, by capillary action,the aqueous vehicle from the overlying layer 5, producing a gradualdrying of said layer.

[0036] The deposition unit 4 comprises a tubular body 8, which isarranged above the surface 3 and transversely to the advancementdirection A and has, in a lower region, a plurality of holes 8 a fordispensing the ceramic mixture, and a pump P for supplying said mixturewhich is associated with the tubular body 8.

[0037] Conveniently, such dispensing holes, not shown in the figures,are distributed along the length of the tubular body 8 with a constantspacing and a width that allow a sufficiently uniform distribution ofthe ceramic mixture on the surface 3.

[0038] As an alternative, the deposition unit 4 may have a conventionalhopper or the like.

[0039] In a first embodiment, shown in FIG. 1, the apparatus 1 comprisesa unit 9 for leveling the layer 5, which is arranged on the surface 3downstream of the deposition unit 4 along the advancement direction Aand comprises at least one leveling blade 10, which is arranged abovethe surface 3 transversely to said advancement direction.

[0040] In the particular embodiment shown, the leveling unit 9 iscomposed of two leveling blades 10, which are arranged in series on thesurface 3 at different distances from said surface.

[0041] In particular, the leveling blade 10 a arranged downstream of theleveling blade 10 b along the advancement direction A is arranged closerto the surface 3 than the leveling blade 10 b.

[0042] However, alternative embodiments of the invention are alsopossible in which the leveling blades 10 are arranged for example sothat they are equidistant from the surface 3 or in which the firstleveling blade 10 encountered by the layer 5 along the advancementdirection A is closer to the surface 3 than the subsequent levelingblade or blades 10, so as to compress said layer.

[0043] The leveling blades 10 can be associated with means for adjustingtheir respective working heights with respect to the surface 3.

[0044] If the apparatus 1 has a plurality of deposition units 4, it ispossible to provide a plurality of leveling units 9 distributed alongthe surface 3, each unit being arranged downstream of a correspondingdeposition unit 4.

[0045] The apparatus 1 can be provided with automatic means for removingthe tubular body or bodies 8 and the leveling blades 10 in case ofmaintenance and/or cleaning of the surface 3.

[0046] The drying unit 6 comprises ventilation means 32 and optionallycomprises heat generation means 33 of the conduction, convection orradiation type, which cooperate with the lower portion of the surface 3.

[0047] In a particular embodiment of the apparatus 1, for example, thedrying unit 6 has a channel 11, which is arranged below the surface 3and feeds below said surface an air stream that is generated by saidventilation means and is heated by appropriate heat generation means ofa conventional type.

[0048] Conveniently, the drying unit 6 has a closed chamber 12 forcontaining a portion of the surface 3 that is arranged above the surface3 directly downstream of the deposition unit 4 and of the correspondingleveling unit 9 along the advancement direction A of said surface.

[0049] The humidity that evaporates from the surface 3 and accordinglyfrom the layer 5 gradually saturates the atmosphere inside the chamber12, so as to hinder initially the drying of the upper part of the layer5, avoiding the formation of defects such as wrinkles or microcracks, atthe upper surface of the strand 7, which coincides with the exposedsurface of the articles being produced.

[0050] Advantageously, the surface 3 comprises at least one first layer13 of material that absorbs the aqueous vehicle contained in the mixturebeing used, which forms the surface on which the layer 5 rests and istherefore in contact with it.

[0051] Said absorbent material is constituted for example by textilefibers, preferably made of cotton or any other fiber adapted to absorbaqueous substances.

[0052] The apparatus 1 further has at least one second layer 14 forsupporting the first layer 13, which is arranged below said first layerat least at the drying unit 6 and is made of an air-permeable material.

[0053] The material of which the second layer 14 is made is preferablymade of a material that has heat-conduction properties, i.e. is of theheat-conducting type.

[0054] In a preferred embodiment of the apparatus 1, the second layer 14is constituted by a metallic mesh of appropriate thickness, so as tosupport the first layer 13, which is constituted by a plurality ofmutually articulated links whose width makes said mesh rigid enough toprovide suitable support for the first layer 13 and allow the air streamgenerated below the surface 3 to strike said first layer.

[0055] The first layer 13 is provided with two side walls 15 forcontaining the mixture layer 5, which protrude upward from said firstlayer and are arranged parallel to the advancement direction A.

[0056] In the particular embodiment shown in FIG. 1, the surface 3 isformed by the active portion of a conventional continuous belt conveyor16.

[0057] The first layer 13 and the second layer 14 are closed in a loop;the second layer 14 winds around two pulleys 17, a driving pulley and adriven pulley, which are supported so that they can rotate aboutrespective horizontal rotation axes by the framework 2, while the firstlayer 13 winds around the second layer 14 so as to constitute said belt.

[0058] In a first embodiment of the surface 3, shown in FIG. 3, thefirst layer 13 and the second layer 14 are mutually coupled by way ofinterposed coupling means 18 and the pulleys 17 actuate the simultaneousadvancement of both layers 13 and 14.

[0059] The coupling means 18 are constituted for example by connectionelements of the threaded or pressure-based type or the like, which aredistributed along the lateral and superimposed edges of the layers 13and 14.

[0060] The means for actuating the first layer 13 and the second layer14 along the advancement direction A mutually coincide and areconstituted by the pulleys 17.

[0061] In this case, the first layer 13 must be made of a material thatis elastic enough to compensate for the different expansion of saidfirst layer with respect to the second layer 14 at the pulleys 17.

[0062] In a second embodiment of the surface 3, shown in FIG. 4, theapparatus 1 comprises first and second actuation means, which areseparate but synchronized, for the advancement of the first layer 13 andof the second layer 14 respectively.

[0063] Conveniently, there are conventional means 31 such as suitablemechanical means provided at pulleys 17 for synchronizing theadvancement of the first and second layers 13 and 14 in order to avoidtheir mutual slippage.

[0064] The apparatus 1 further has means 19 for tensioning the firstlayer 13.

[0065] The first actuation means are constituted by two flexibleelements 20, which are constituted by respective chains that are closedin a loop and wound around respective pairs of driving and drivensprockets or pulleys 30, which are supported, so that they can rotateabout respective horizontal axes, by the framework 2.

[0066] The flexible elements 20 are arranged on opposite sides of thesurface 3 and are associated with the first layer 13 by interposingtensioning means 19.

[0067] The flexible elements 20 are supported so that they can slidewithin respective guiding profiles 21 that are associated with theframework 2.

[0068] The tensioning means 19 comprise elastic traction meansconstituted by a plurality of springs 22 that are distributed along thelateral edges of the first layer 13.

[0069] The first layer 13 protrudes laterally from the second layer 14and has a plurality of slots, not shown in the figures, which aredistributed along the corresponding lateral edges and in which thehook-like ends of respective springs 22 are inserted, the opposite endsof said springs being inserted in corresponding openings, not shown inthe figures, formed in brackets 23 that are fixed to the flexibleelements 20.

[0070] In this case, the second actuation means are instead constitutedby two pulleys, not shown in the figures, around which the second layer14 is wound in a loop.

[0071] The framework 2 further comprises supports 24, which are arrangedbelow the surface 3 and slidingly support the second layer 14.

[0072] In a second embodiment, shown in FIG. 5, the apparatus 1 hasmeans 25 for vibrating at least the first layer 13, which are arrangedbelow the surface 3 and proximate to the deposition unit 4 so as toachieve uniform distribution of the layer 5 on said surface as well ashomogenization of said layer.

[0073] The action of the vibrating means 25, moreover, facilitates theelimination of any air bubbles retained by the slurry, improving thequality of the strand 7 obtained by drying.

[0074] The vibrating means 25 are preferably interposed between thedeposition unit 4 and the drying unit 6 and can be constituted forexample by a vibrating surface of the mechanically-actuated, ultrasonicor other type, which is tangent below the first layer 13.

[0075] The apparatus 1 shown in FIG. 5 does not have the leveling unit 9described above, but as an alternative said unit can be provided.

[0076] The first and second actuation means are separate butsynchronized, since said synchronization means are interposed so as toavoid mutual slippage between the layers 13 and 14.

[0077] The first actuation means comprise a plurality of first pulleys26, at least one of which is a driving pulley, around which the firstlayer 13 is wound in a loop.

[0078] The active portion of the second layer 14 is tangent in a lowerregion with respect to the active portion of the first layer 13, so asto support it at least at the drying unit 6.

[0079] The second actuation means comprise a second driving pulley 27and a second driven pulley 28, around which the second layer 14 is woundin a loop, said pulleys being arranged inside the loop formed by thefirst layer 13.

[0080] Downstream of the second layer 14 there is a connecting surface29 that supports the end portion of the first layer 13.

[0081] If there are a plurality of deposition units 4, it is possible toprovide a plurality of vibrating means 25 arranged at respectivedeposition units 4.

[0082] The method according to the invention, performed with the aid ofthe apparatus 1, comprises at least one step for depositing by pouringat least one layer 5 of a ceramic mixture that comprises an aqueousvehicle on the surface 3; at least one step for drying the lower portionof the surface 3 at the layer 5, so as to achieve at least partialevaporation of the aqueous vehicle absorbed by said surface, withconsequent at least partial drying of the layer 5 to obtain a continuousstrand 7 of plastic ceramic material; and a step for cutting said strand7 in order to obtain a plurality of ceramic articles having the chosendimensions.

[0083] The method according to the invention may further provide for astep for separating the strand 7 from the surface 3 and for transferringsaid strand onto an auxiliary working surface, not shown in the figures,said step being performed ahead of the cutting step.

[0084] The drying step consists in generating a stream of forced airbelow the surface 3 and preferably in applying heat to the lower side ofthe surface 3 by conduction or convection or radiation.

[0085] Drying of the surface 3 occurs in a controlled manner, so thatthe strand 7 retains a residual humidity that gives it the plasticityrequired to perform the separation and cutting steps.

[0086] The method according to the invention further comprises at leastone step for leveling the deposited layer 5.

[0087] As an alternative to the leveling step, or as an additionthereto, the method according to the invention can provide for a stepfor vibrating the deposited layer.

[0088] In an alternative embodiment, the method provides for theexecution of a plurality of successive steps for depositing respectivelayers 5, the first layer 5 being deposited on the surface 3 and eachsuccessive layer 5 being deposited on the previously deposited layer 5.

[0089] In this case, after one or more deposition steps it is possibleto provide a step for leveling the thickness of the deposited layer 5and/or a step for vibrating each deposited layer 5.

[0090] In the method according to the invention, the step for drying thesurface 3 can be performed simultaneously with the deposition step orafter said deposition step.

[0091] It is then possible to provide a step for glazing and/ordecorating the last deposited layer 5 and a step for rolling the strand7, performed before the cutting step.

[0092] The resulting articles then follow the conventional productionprocess, which substantially consists of drying, firing, sorting andpacking.

[0093] In practice it has been found that the described inventionachieves the proposed aim and object.

[0094] The invention thus conceived is susceptible of numerousmodifications and variations, all of which are within the scope of theappended claims.

[0095] All the details may further be replaced with other technicallyequivalent ones.

[0096] In practice, the materials used, as well as the shapes and thedimensions, may be any according to requirements without therebyabandoning the scope of the protection of the appended claims.

[0097] The disclosures in Italian Patent Application No. MO2003A000174from which this application claims priority are incorporated herein byreference.

What is claimed is:
 1. A method for forming substantially plate-shapedceramic articles, comprising: at least one step for deposition bypouring of at least one layer of a ceramic mixture that comprises anaqueous vehicle on a substantially absorbent transfer surface adapted todraw said aqueous vehicle; at least one step for drying at least a lowerportion of said surface so as to achieve at least partial evaporation ofthe aqueous vehicle absorbed by said surface, with consequent at leastpartial drying of said mixture layer in order to obtain a continuousstrand of plastic ceramic material; and a step for cutting said strandinto a plurality of ceramic articles.
 2. The method of claim 1, whereinsaid drying step consists in generating a stream of forced air belowsaid surface.
 3. The method of claim 1, wherein said drying stepconsists in applying heat below said surface.
 4. The method of claim 1,further comprising at least one step for vibrating said depositedmixture layer.
 5. The method of claim 1, further comprising at least onestep for leveling said deposited mixture layer.
 6. The method of claim1, wherein said deposition step is constituted by successive sub-stepsfor deposition of respective layers of said mixture, with a first one ofsaid layers being deposited on said surface and each successive layerbeing deposited onto the previously deposited layer.
 7. The method ofclaim 6, further comprising a plurality of vibrating steps for vibratingeach deposited layer carried out after respective deposition steps. 8.An apparatus for forming substantially plate-shaped ceramic articles,comprising a framework for supporting a substantially absorbent transfersurface; at least one deposition unit for depositing by pouring at leastone mixture layer of a ceramic mixture that comprises an aqueous vehicleon said surface; at least one drying unit for drying at least the lowerportion of said surface so as to achieve at least a partial evaporationof the aqueous vehicle absorbed by said surface, with consequent atleast partial drying of said mixture layer in order to obtain acontinuous strand of plastic ceramic material; and a cutting unit forcutting said strand into a plurality of ceramic articles.
 9. Theapparatus of claim 8, wherein said transfer surface comprises at leastone first layer made of a material adapted to substantially absorb saidaqueous vehicle.
 10. The apparatus of claim 9, wherein said absorbentmaterial is constituted by textile fibers constituted by cotton or anyother fiber adapted to absorb aqueous substances.
 11. The apparatus ofclaim 9, comprising at least one second layer for supporting said firstlayer, which is arranged below said first layer and is constituted by amaterial that is substantially permeable to air.
 12. The apparatus ofclaim 1 1, wherein said second layer is constituted by a material withheat-conducting properties.
 13. The apparatus of claim 12, wherein saidsecond layer is constituted by a metal mesh constituted by a pluralityof mutually articulated links.
 14. The apparatus of claim 11, furthercomprising coupling means, which are interposed between said first andsecond layers and are adapted to mutually couple said layers.
 15. Theapparatus of claim 9, wherein said first layer comprises at least onepair of side walls for containing said mixture layer.
 16. The apparatusof claim 1 1, comprising first and second synchronized actuation meansfor actuating advancement of said first and second layers respectively.17. The apparatus of claim 16, comprising tensioning means fortensioning said first layer.
 18. The apparatus of claim 17, wherein saidtensioning means comprises elastic traction means.
 19. The apparatus ofclaim 16, wherein said surface is formed by an active portion of acontinuous belt conveyor.
 20. The apparatus of claim 19, comprising twopulleys, a driving pulley and a driven pulley, which are rotatablysupported by said framework, said first and second layers being closedin a loop, with the second layer being wound around said pulleys, thefirst layer being wound around said second layer so as to constitutesaid belt.
 21. The apparatus of claim 20, wherein said first actuationmeans are constituted by two flexible elements, which are closed in aloop and wound around respective pairs of said pulleys that arerotatably supported by said framework, said flexible elements beingarranged laterally to said first layer and being associated with saidfirst layer by interposing said tensioning means.
 22. The apparatus ofclaim 11, comprising at least one leveling unit for leveling saiddeposited mixture layer, which is arranged on said surface downstream ofsaid deposition unit along an advancement direction of said surface. 23.The apparatus of claim 22, wherein said leveling unit comprises at leastone leveling blade, which is arranged above said surface andtransversely to the advancement direction of said surface.
 24. Theapparatus of claim 23, wherein said deposition unit comprises a tubularbody, which is arranged above said surface and lies substantiallytransversely with respect to the advancement direction of said surfaceand is provided in a lower region with a plurality of holes fordispensing said mixture, and with a pump for feeding said mixture towardsaid tubular body.
 25. The apparatus of claim 24, comprising vibratingmeans for vibrating at least said first layer, said vibrating meansbeing arranged at least at said deposition unit.
 26. The apparatus ofclaim 25, wherein said drying unit comprises ventilation means, whichcooperate with a lower portion of said surface.
 27. The apparatus ofclaim 26, wherein said drying unit comprises heat generation means thatcooperate with the lower portion of said surface.
 28. The apparatus ofclaim 27, wherein said drying unit comprises at least one chamber forcontaining a portion of said surface, said chamber being arranged abovesaid surface downstream of said deposition unit along the advancementdirection of said surface.
 29. The apparatus of claim 11, comprising aplurality of said deposition units distributed along said surface. 30.The apparatus of claim 29, further comprising a plurality of levelingunits arranged downstream of respective deposition units.
 31. Theapparatus of claim 30, further comprising a plurality of vibrating unitsfor vibrating at least said first layer, each arranged downstream of arespective deposition unit.